Controller-induced parasitic torque ripples in a PM synchronous motor

Permanent magnet (PM) synchronous machines with a sinusoidal back electromotive force are ideally capable of torque-ripple-free operation. However, parasitic torque ripples can still be induced from motor design and controller implementation. This paper focuses on a systematic analysis of possible sources of torque ripple in a PM synchronous machine drive resulting from limitations in the motor controller. It takes into account the effects of finite encoder resolution, controller CPU word length, current sensing errors, and inverter pulsewidth-modulation switching. Approaches for analyzing and calculating torque ripple from each of those sources have been developed. Characteristics of the various parasitic torque ripples are discussed. Experimental and simulation data to verify important results are also presented.